Control device for machine tool performing oscillation cutting

Abstract

A control device includes a command block timing detection unit for detecting arbitrary timing between adjacent command blocks, based on a machining program, which includes a plurality of command blocks, of a machine tool. A feed axis control unit includes a learning controller, and a determination unit that determines whether or not a current time is in the arbitrary timing between the adjacent command blocks, and stops oscillation of at least one feed axis based on the determination.

What is claimed is: 
     
       1. A control device for controlling a machine tool for machining an outer peripheral surface or an inner peripheral surface of a workpiece using a tool, the machine tool including a main spindle for relatively rotating the workpiece and the tool about a central axis line of the workpiece, and at least one feed axis for relatively feeding the tool and the workpiece along a generatrix of the outer peripheral surface or the inner peripheral surface of the workpiece, the control device comprising:
 a position command generation unit for generating a position command for the feed axis, based on a relative rotation speed between the workpiece and the tool, and a relative feed speed between the tool and the workpiece; and 
 a feed axis control unit for controlling the feed axis by the position command, wherein 
 the feed axis control unit includes an oscillation command generation unit for generating an oscillation command for the feed axis based on the rotation speed and the position command, such that an oscillation frequency becomes a positive non-integer multiple of the rotation speed, and such that the tool intermittently machines the workpiece, and the feed axis control unit controls the feed axis based on a composite command obtained by adding the oscillation command to a positional deviation that is a difference between the position command and an actual position of the feed axis, 
 the control device further includes a command block timing detection unit for detecting arbitrary timing between adjacent command blocks, based on a machining program, including a plurality of command blocks, of the machine tool, and 
 the feed axis control unit further includes:
 a learning controller for performing learning control in which a correction amount of the composite command is calculated based on an oscillation phase calculated from the oscillation command, and the composite command, and the correction amount is added to the composite command; and 
 a determination unit for determining whether or not a current time is in the arbitrary timing between the adjacent command blocks, and for stopping oscillation of the feed axis based on the determination. 
 
 
     
     
       2. The control device according to  claim 1 , wherein the arbitrary timing between the adjacent command blocks is arbitrary timing in a time period between the start of deceleration in an anterior command block of the adjacent command blocks and the completion of acceleration in a posterior command block. 
     
     
       3. The control device according to  claim 2 , wherein when the determination unit determines that the current time is in the arbitrary timing between the adjacent command blocks, the determination unit stops oscillation of the feed axis for a certain first period of time, or a certain first number of oscillations. 
     
     
       4. The control device according to  claim 2 , wherein when the determination unit determines that the current time is in the arbitrary timing between the adjacent command blocks, the determination unit delays stopping oscillation of the feed axis by a certain second period of time, or a certain second number of oscillations. 
     
     
       5. The control device according to  claim 2 , wherein the command block timing detection unit notifies the determination unit of the arbitrary timing between the adjacent command blocks, a certain third period of time or a certain third number of oscillations in advance. 
     
     
       6. The control device according to  claim 1 , wherein the determination unit stops oscillation of the feed axis only in a last machining pass. 
     
     
       7. The control device according to  claim 1 , wherein stopping the oscillation command includes disabling the learning control, or setting the oscillation command at zero, as well as disabling the learning control. 
     
     
       8. The control device according to  claim 1 , wherein the oscillation command generation unit generates the oscillation command in which an oscillation amplitude is subtracted, as an offset value, from a cosine reference axis line. 
     
     
       9. The control device according to  claim 1 , wherein the oscillation command generation unit generates an oscillation frequency of the oscillation command based on the rotation speed, such that the oscillation command is half a period out of phase, whenever the workpiece or the tool makes one rotation, and generates an oscillation amplitude of the oscillation command based on the rotation speed and the position command. 
     
     
       10. The control device according to  claim 1 , wherein the oscillation command generation unit generates an oscillation frequency and an oscillation amplitude of the oscillation command, such that a torque of the feed axis does not exceed a predetermined value. 
     
     
       11. The control device according to  claim 1 , wherein the oscillation command generation unit generates an oscillation frequency and an oscillation amplitude of the oscillation command, based on a control range of the learning control, such that learning converges. 
     
     
       12. The control device according to  claim 1 , wherein the oscillation command generation unit generates an oscillation frequency and an oscillation amplitude of the oscillation command, based on a desired length of a cutting chip produced by the tool machining the workpiece. 
     
     
       13. The control device according to  claim 1 , wherein the workpiece has a corner that is not continuous from a radially outermost portion of the workpiece, inside the radially outermost portion in a radial direction, in a section along the central axis line.